This invention relates generally to high frequency feed-through electrical filters and, more particularly, to electrical filters using multiple capacitors constructed of planar dielectric devices.
Capacitive coupling to an electrical conductor at high frequencies is a critical element in passive low pass filters. The fundamentals of low pass filters are well established in the prior art. Design of the capacitive elements for such filters is a challenge, particularly at high frequencies. Discrete leaded capacitors are not suitable at high frequencies because of the inherent self inductance associated with even the shortest of leads. Any practical connection length in the capacitive circuit will interfere with the proper operation of a low pass filter, due to the inductance impedance of these leads.
Because of these deleterious effects, high frequency capacitors have here-to-fore been constructed using an annular configuration, in which the inside diameter effectively is one electrode of a capacitor, and the outside edge constitutes the other electrode of the capacitor. The annular volume is used to house a dielectric material. This variety of electrodes surface configurations to maximize the area affected by the dielectric. However, known annular configurations present several problems. In the cases in which ceramic dielectric is used, the resultant configurations are subject to breakage, if there is relative motion between a housing and an electrode. Also, the dielectric is difficult to form, and can be limited in dielectric volume because of practical size limitations. Furthermore, the exact geometry and thus capacitance value is difficult to control. For those cases in which the capacitor is of a wound film construction, voids and defects are chronic problems. The inspection and repair of wound film types is extremely difficult.
The object of this invention, therefore, is to provide an improved electrical filter.